A switch-operated therapeutic agent delivery device can provide single or multiple doses of a therapeutic agent to a patient by activating a switch. Upon activation, such a device delivers a therapeutic agent to a patient. A patient-controlled device offers the patient the ability to self-administer a therapeutic agent as the need arises. For example, the therapeutic agent can be an analgesic agent that a patient can administer whenever sufficient pain is felt.
One means of patient controlled analgesia is patient controlled intravenous infusion, which is carried out by an infusion pump, which is pre-programmed to respond to the instructions of a patient within certain pre-determined dosing parameters. Such intravenous infusion pumps are commonly used for control of postoperative pain. The patient initiates infusion of a dose of analgesic, which is typically a narcotic, by signaling a control unit. The unit receives the signal and, if certain conditions are met, begins infusion of the drug through a needle that has been inserted into one of the patient's veins.
Another form of patient controlled analgesia is electrotransport (e.g., iontophoresis, also referred to as iontophoretic drug delivery). In electrotransport drug delivery, a therapeutic agent is actively transported into the body by electric current. Examples of electrotransport include iontophoresis, electroosmosis and electroporation. Iontophoresis delivery devices typically comprise at least two electrodes connected to reservoirs, a voltage source, and a controller that controls delivery of the therapeutic agent by applying the voltage across the pair of electrodes. Usually at least one of the reservoirs contains a charged therapeutic agent (drug), while at least one reservoir contains a counter-ion and no therapeutic agent. The therapeutic agent, which is a charged species, is driven from the reservoir containing the therapeutic agent and into and across the skin into the patient to whom the reservoirs are attached.
In addition to therapeutic agent, the reservoirs may contain other charged and uncharged species. For example, the reservoirs are often hydrogels, which contain water as a necessary constituent. The reservoirs may also contain electrolytes, preservatives, antibacterial agents, and other charged and uncharged species.
For safety reasons, it is essential that any patient-controlled drug delivery device, and particularly an electrotransport device delivering a therapeutic agent (e.g., an opoid analgesic such as fentanyl) be tightly regulated to prevent the inadvertent delivery of agent to a patient. For example, short circuits in the device may result in erroneous, additional delivery of drug. Since patient-activated dosing systems must include a dose switch that is selected, e.g., pushed, by a patient to deliver a dose, one particularly vulnerable aspect is this switch. A short circuit in the dose switch circuit could be interpreted by control logic (e.g., processor) of the device as valid dose switch presses, and potentially cause the system to deliver a dose even without a valid patient request. Such short circuits could be caused by contamination or corrosion.
Described herein are methods and apparatuses (e.g., system and devices) that validate the integrity of a dose switch circuit and signal characteristics prior to initiating a dose. In particular, the apparatuses and methods described herein perform validation before each dose initiation, and the validation process (e.g., measurements used to determine if the switch is properly functioning) do not interfere with normal operation, including in particular actual presses of the dose switch. Finally, the apparatus and methods described herein are demonstrably reliable to a high degree of certainty. These apparatus and methods may therefore address the issues raised above.